The present invention relates to a method and a tool for bonding external leads of an IC component mounted on a circuit substrate with electrodes of the circuit substrate.
Conventionally, in bonding lead wires of an IC component mounted on a circuit substrate with electrodes of the circuit substrate, a reflow method for melting a cream solder on each electrode has generally been employed. The reflow method is not convenient in some cases because the IC component or a liquid crystal panel to be bonded with the IC component is exposed to a high temperature when passing through a reflow apparatus, and the equipment becomes bulky in structure.
In the meantime, for bonding leads of an IC component which is low in thermal resistance, it has been proposed to provide bonding metallic layers on electrodes of a substrate by plating solders, placing leads of the IC component on the bonding metallic layers and then pressing the leads against the electrodes with a heating tool. That is, a bonding method for bonding the leads via the bonding metallic layers by heat and pressure has been practiced. In this case, such a heating tool has been built in to the substrate or a pulse current has been supplied to instantaneously heat the leads.
According to the above bonding method using the heating tool, when the leads are heated by the high-temperature heating tool, the flux of the bonding metal is adhered to the heating tool, therefore making uniform heating and pressuring of the leads impossible. Highly reliable bonding cannot be achieved. Moreover, since the substrate and IC component may be expanded when bonding with heat, when the substrate is cooled after bonding the leads of the IC component may be cut or disconnected at the opposite side of the surface where the IC component is soldered and bonded with the liquid crystal. Furthermore, a heating tool in which a pulse current flows is easily deformed by heat. When all the leads extending from one side of the IC component are to be wholly pressed by the heating tool, it is difficult to ensure the parallelism of the heating tool to the circuit substrate, due to the recent trend that IC components are formed large in size. Adverse influences occur, such as warping of the substrate or an irregularity of the thickness of the bonding metallic layer, resulting in the generation of imperfectly bonded leads.
Next, a conventional bonding method of TAB electronic components will be depicted hereinbelow.
FIG. 10 is an explanatory diagram of the conventional bonding method of TAB electronic components. In FIG. 10, reference numeral 31 is a liquid crystal panel and reference numeral 32 represents a TAB electronic component such as a LSI to be driving mounted according to the TAB method. An anisotropic conductive sheet 33 is attached to a connecting terminal part of the liquid crystal panel 31. More specifically, the anisotropic conductive sheet 33 mounted at the connecting terminal part of the liquid crystal panel 31 is temporarily fixed with some pressure and heat. Then, after bonding leads of the TAB electronic component 32 are registered with the connecting terminals of the liquid crystal panel 31, the electronic component 32 is actually heated and pressured to be perfectly bonded with the liquid crystal panel 31.
In the above-described method, however, specific equipment is required to register and temporarily fix the long anisotropic conductive sheet to the liquid crystal panel. It is also necessary to feed and mount the TAB electronic component immediately after the anisotropic conductive sheet is temporarily fixed to the liquid crystal panel so as to prevent deterioration of the anisotropic conductive sheet and the adhesion of dust to the anisotropic conductive sheet.